Volunteer monitoring began at Trout Lake in 1996 and continued through 2008, after which it was discontinued. The data indicated this lake was strongly colored and relatively high in primary productivity (borderline eutrophic) with good to fair water quality. Productivity decreased over time, with the trend moderately well correlated.
Profile data showed thermal stratification was constant through summer, and sedimentary phosphorus release added significantly to deep water concentrations. Nitrogen to phosphorus ratios in the upper water were above 20:1, which generally favors other algal species over bluegreens.

Trout Lake has a street end public access from which boats can be launched, and residents should keep a close eye on aquatic plants growing nearshore to catch early infestations of aquatic noxious weeds.

This bathymetric map shows contour lines of equal depth, similar to a topographic map would for mountains and valleys. The red 'X' marks the location where water quality samples are taken.

This map shows the area of the watershed relative to the area of the lake. Generally speaking, the larger a watershed is relative to a lake, the greater the influence land use practices on lake water quality.

Through a combination of efforts by volunteer lake monitors and King County staff,
data relating to physical, chemical, and biological aspects of the lake have been
collected for most lakes. The King County Lake Stewardship Program analyzes data
to track long-term water quality trends in small lakes in western King County.

View or Download DataUse this tool to view or download data from the lake in tabular format. You can
define date ranges and select which parameters to view or download.

Chart DataUse the charting tool to look at graphs showing single parameters for a single
water year at a time.

Water quality over time
A common method of tracking water quality trends in lakes is by calculating the
“trophic state index” (TSI) (Carlson, 1977) and testing the values for positive or
negative trends over time. TSI indicators predict the biological productivity of the lake
based on water clarity (Secchi) and concentrations of total phosphorus (TP) and chlorophyll
a (Chlor). Generally at least 8 years of data without major lake management
activities are needed to have confidence in a significant trend.

The average of these three TSI indicators during the growing season can be used
to place lakes in one of three broad categories:
<40 = oligotrophic (low productivity),
40 to 50 = mesotrophic (moderate productivity)
>50 = eutrophic (highly productive).